The invention relates to a transmission system for transmitting video or other information over a network, and more particularly to a transmission system for efficiently, selectively and interactively transmitting video and other information over a single twisted copper wire pair in the Public Switched Telephone Network (PSTN) at a variable rate or in a variable mode.
It has recently become possible to provide wired transmission of full-motion digitized video programming, rather than still frame or limited video conferencing, without the use of dedicated leased, wide bandwidth circuits and T1 lines. In particular, it has become possible to provide for the cost effective routing and distribution of a large amount of video or other data at high speed and in real time using the existing copper plant. For example, U.S. Pat. Nos. 5,341,474 and 5,371,532 to Gelman et al discuss a xe2x80x9cstore-and-forwardxe2x80x9d architecture and method for distributing information to subscribers and U.S. Pat. No. 5,247,347, issued to L. Litteral et al on Sep. 21, 1993 and assigned to the assignee of the present invention, discusses a method of providing video-on-demand (VOD) services with VCR type functional control of the programming.
In the systems discussed in these three patents, a menu of programming information is accessible at the subscriber""s premises. The subscriber may transmit order requests via the PSTN to the independent information providers. Information programs may be accessed and transmitted to the subscriber directly from an information provider or through a video buffer located at a central office (CO) serving the subscriber.
The information provider transmits coded digital data over wideband PSTN to a central office. The data may be buffered at the central office for transmission over a POTS (plain old telephone service) line to the subscriber using a video gateway. An access concentrator/packet switch at the central office receives the order request from the subscriber loop. A video gateway in turn is responsive to the order request for producing routing data. A file server, responsive to requests received from the video gateway, obtains selected information from the digital information storage medium. A circuit or ATM cross-connect switch in turn is responsive to the routing data for transferring the information from the file server to the subscriber loop transmission means.
A subscriber in such a system may use either a standard telephone instrument over the PSTN or a dedicated control device over an X.25/ISDN packet network to order the information program. The dedicated control device is either a settop box which is located at a television set of the subscriber and which permits a display of the program menu on the television screen or a computer with appropriate control boards.
Connectivity between the central office and the subscriber for transmission of data is provided by one of a number of different interface units, such as an asymmetrical digital subscriber line (ADSL) interface or a high bit rate digital subscriber line (HDSL) interface. ADSL systems are generally preferable to bi-directional HDSL systems for services such as video-on-demand in which the amount of information transmitted in one direction is much greater than the amount of information transmitted in the opposite direction. ADSL systems provide a cost effective and bandwidth efficient platform for receiving or transmitting a large volume of information at high speed in a single direction using the existing copper plant. An asymmetrical communication transport provides high bandwidth for fast transfer of bulk data in one direction, while a slow transmission rate is used for bi-directional communication. Typically, a request for data requires very little data transfer in the upstream direction and the data delivery involves high data traffic in the downstream direction. In addition, ADSL systems are generally capable of transmitting over longer distances than HDSL, do not interfere with POTS or ISDN communications and therefore require only a single copper pair.
T1 communication enables simultaneous high speed digital transmission of bulk data in both directions, but requires special wiring and circuitry and exceeds requirements for data network applications in which high bulk data transfer occurs only in one direction at a time. Existing video conferencing transceivers and HDSL systems permit bi-directional transmission at high bit data rates.
The data rates of the channels in conventional ADSL systems are typically predetermined according to the structure of the ADSL interface units. Therefore, although previous systems may be well suited for some services such as video-on-demand, they are not well suited for other services in which the nature and amount of data and control signal transfer is substantially different or changes frequently. Specifically, the two-way control channel may be unacceptably slow for services such as interactive multi-media, distance learning, or accessing a server in a remote local area network (LAN) over a POTS line using a single copper pair. One or more of these services may require a bi-directional control channel of up to, for example, 384 kbps in order to allow substantially real-time communications so that a subscriber is not waiting for information to be transmitted.
Furthermore, systems which provide services such as video-on-demand and home shopping typically only provide for the transfer of video programming or other data in a single direction from a VIP or other information provider to a subscriber. They may not provide significant bi-directional capability, full connectivity amongst all of the subscribers on the network, or multi-cast transmission capability which can be point-to-point or point-to-multipoint for distance learning, video phone etc.
Accordingly, it is a broad object of the invention to controllably operate in one of a plurality of different modes and at any one of a plurality of different bit rates so as to provide a single transmission platform which may support a plurality of different services, including but not limited to, video on demand and reliable bi-directional communications at data rates greater than 16 kbps.
Another object of the invention is to provide an asymmetrical flow of information wherein the direction of the asymmetrical flow of information can be simply and easily reversed.
Still another object of the invention is to simply and easily vary the bit rates of the upstream and downstream channels, or the modes of the transceivers, of an ADSL network.
Another object is to either automatically control bit rate or mode by the CO or selectively control bit rate or mode by the subscriber.
A further object of the invention is to provide a high speed reversible channel for receiving and sending unidirectional data/video.
Still another object is to provide a truly bi-directional fractional T1 service using a transceiver that transmits only a fractional T1.
It is a further object of the invention to provide a full service information network over the existing copper plant of telephone wires by connecting to a computer network and performing format conversion and multi-cast transmission in real time.
In order to achieve the above objects, this invention adds capabilities to present networks by providing an ADSL having adjustable variable rate functionality (ADSL/AVR). A controllable transceiver in the ADSL/AVR allows the communication rate to be selected from 2xc3x9764 KB up to 1.5 Mb/s or 6.2 Mb/s into a digital cross connect system or ATM edge device or switch. Such a network has the advantages of conventional ADSLs, while allowing the data rate of the reverse control signaling channel to be controllably increased so as to have a higher rate transmission than ADSL in a bi-directional mode.
A preferred embodiment of the invention uses a terminating unit which has a T1 interface on one side and a variable rate interface on the other side. A digital cross connect system has at least one 1/1 cross-connect to cross connect T1s and a plurality of 1/0 cross connects to cross connect fractional parts of T1s (DSOs) in order to aggregate or groom services in the backbone network between the 1/0 DCSs and provide more efficient transport across the network.
Other embodiments of the invention use an ATM, Frame Relay, or SMDS network at the central office end. Ethernet interfaces are used to facilitate transport to a personal computer at the remote end and LAN/WAN connections to ATM, Frame Relay, or SMDS switching at the central office end.
This variable rate/variable mode ADSL service will accommodate access to a wide variety of information providers such as the Internet or other data networks through which data from servers are to be retrieved. The service has applicability in various contexts such as telecommuting and banking services. The ADSL service can also be used in an office building LAN or between house pairs.
In addition to variable bit rates for the control channel, the invention enables at least two modes for the ADSL transceivers, one providing bi-directional communications and the other providing asymmetrical communications such as video-on-demand. Each ADSL transceiver is either a discrete multi-tone (DMT), CAP or DWMT transceiver comprising identical programmable chip sets in which different firmware may be downloaded to enable the different rates and different modes.
In accordance with a further aspect of the invention, the transmission bit rate may be asymmetrical in selectively changeable directions so that parties to a communication session can individually exchange bulk data transmission in both directions. The ADSL transceivers may be responsive to a control signal transmitted in the upstream channel which indicates that the direction in which data is transmitted should be reversed.
The above and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.